1. Field of the Invention
The present invention relates to a curable silicone composition, in particular to a silicone composition useful as various release agents and the like capable of forming coatings with a low surface energy and its cured product.
2. Description of the Prior Art
For pressure sensitive tapes and pressure sensitive labels, pressure sensitive adhesives are used. Where the pressure sensitive adhesive is used, a release agent comprising, for example, a curable silicone composition, etc. is also often used.
For example, a rolled pressure sensitive tape is required to be unrolled when subjected to use, and therefore release coating has been formed on the back of the tape so that the unrolling operation can be conducted smoothly and a pressure sensitive agent may remain on one side of the tape without fail. Pressure sensitive labels in the form of sheet have release coating on the surface of their backing so that the labels can be peeled smoothly from the backing when subjected to use and no pressure sensitive agent may remain on the backing.
Such release coatings need to adhere to the back of the tapes or the surface of the backing and to have sufficient cohesion so that a pressure sensitive agent may not immigrate. Release agents capable of forming coatings with such a good release property include curable silicones disclosed in Japanese Pre-examination Patent Publication (Kokai) No. 62-225581(1987), Japanese Pre-examination Patent Publication (Kokai) No. 63-320(1988), etc. These curable silicones contain as a major component an organopolysiloxane having a fluorine-containing substituent represented by the formula: C.sub.n F.sub.2n+1 CH.sub.2 CH.sub.2 -- (where n is an integer of 1 or more).
By the way, in recent years, pressure sensitive adhesive agents containing as a major component a dimethylpolysiloxane are used for wide purposes because of their heat resistance, cold resistance, chemical resistance and electrical insulation properties. Since the pressure sensitive agents are non-toxic, they are also used in the medical field.
The release agents comprising conventional curable silicones cannot offer a sufficient release property, however, because the pressure sensitive adhesive of this type have extremely strong adhesion. Particularly, where a tape or a label on which this pressure sensitive agent is used is stored for a long time, peel force required to peel it from the back of the tape or the backing would increase seriously, so that the pressure sensitive agent layer or the release agent layer is broken when peeling is conducted, and thereby the pressure sensitive tape (or the label) would become useless. The release agent composed of the above-mentioned silicone containing as a major component an organopolysiloxane having a fluorine-containing substituent, does not offer satisfactory release properties in this respect, either.